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IC 9207 



BUREAU OF MINES 
INFORMATION CIRCULAR/1988 



(2 3^5 




A Seal Breaching Operation in Quinland 
Coal Mine: A Case Study 



By Diane M. Doyle-Coombs and Randy Hansford 



StNTj 



5?u 



UNITED STATES DEPARTMENT OF THE INTERIOR 



Information Circular 9207 



A Seal Breaching Operation in Quinland 
Coal Mine: A Case Study 



By Diane lA. Doyle-Coombs and Randy Hansford 



UNITED STATES DEPARTMENT OF THE INTERIOR 
Donald Paul Hodel, Secretary 

BUREAU OF MINES 
T S Ary, Director 



,of> 






^^' 



Library of Congress Cataloging in Publication Data: 



Doyle-Coombs, D. M. (Diane M.) 

A seal breaching operation in Quinland Coal Mine. 

(Bureau of Mines information circular; 9207) 

Bibliography: p. 12. 

Supt. of Docs, no.: I 28.27:9207 

1. Mine filling— West Virginia. 2. Abandoned coal mines— Environmental as- 
pects—West Virginia. I. Hansford, Randy. II. Title. III. Series: Information circular 
(United States. Bureau of Mines); 9207. 

^TN2 95.U4 [TN292] 622 s [622'.8] 88-600214 



CONTENTS 

Page 

Abstract 1 

Introduction 2 

Background 2 

Detection of mine fire 5 

Seal breaching 6 

Using tracer gas to understand air migration patterns through abandoned area 8 

Predicting gas concentrations 10 

Discussion 11 

Summary 12 

References 12 

Appendix A.-Mine fire sampling plan 13 

Appendix B.-Completion plan 15 

Appendix C.-MSHA approved plan for mine unsealing if continuous monitoring system failed 16 

Appendix D.- Volume calculation behind sealed area 17 

Appendix E.-Calculations of purge times 18 

Appendix F— Calculations of purge time after increase in air volume 19 

Appendix G.-Tracer gas released at 2 North and recovered at 1 North 20 

Appendix H.-Velocity calculations inby seals 21 

ILLUSTRATIONS 

1. Quinland Mine map 3 

2. Quinland Mine 1 and 2 North Main Seals 4 

3. Borehole locations in 2 North 6 

4. Projected mine development 7 

5. Temporary ventilation controls in 2 East 7 

6. SFg concentration in 1 North 9 

7. 1 North CH4 decay curve 10 

8. Concentration in 1 North-COj, O2, Nj, and CO 11 

C-1. Location of checkpoints 16 

TABLES 

1. Average gas concentrations behind seals 5 

2. Borehole descriptions 5 

3. Gas concentrations in number 2 borehole of 2 North after injection of 98 st of CO2 5 

4. Average gas concentrations behind seals and pressure differential across seals prior to breakthrough ... 7 





UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 


cfm 




cubic foot per minute 










L/mol 


hter per mole 


cfm/in, 


w.g. 


cubic foot per minute 


per 


inch, 


water 


gauge 


min 


minute 


fpm 




foot per minute 










mL 


milliliter 


ft 




foot 










mol 


mole 


ft^ 




square foot 










pet 


percent 


ft^ 




cubic foot 










ppm 


part per miUion 


g 




gram 










psi 


pound per square inch 


g/mol 




gram per mole 










St 


short ton 


h 




hoiu- 










Vdc 


volt, direct current 


in 




inch 










w.g. 


water gauge 


L 




liter 










yr 


year 



A SEAL BREACHING OPERATION IN QUINLAND COAL MINE: 

A CASE STUDY 



By Diane M. Doyle-Coombs^ and Randy Hansford^ 



ABSTRACT 

In late July 1985, ciir samples from a sealed portion of the Quinljmd coal mine in West Virginia 
showed the presence of carbon monoxide (CO). Mine Safety and Health Administration (MSHA) 
personnel concluded that a fire was burning behind the seals. Since an imminent danger existed, the 
mine operator was given a closure order. 

The gases behind the seeds were monitored and almost 2 million ft^ of carbon dioxide (COj) gas was 
pumped into the sealed area to stabilize the environment. Sixteen days after the closure order was 
issued, MSHA allowed the mine to return to production. 

Approximately 1 yr later, mine management submitted a seal breaching request to MSHA in order 
to drive a set of entries to further develop the mine. The Bureau of Mines established a s£unpling 
strategy and monitored gases from behind the sealed area during the breaching operation imtil the 
atmosphere was safe. This report is an account of the seal breaching conducted by the mine, MSHA, 
and the Bureau. The logistics of this event, the sampling strategy, and the equations applied could be 
used by the mining industry in future breachings or mine recovery operations. Time to reenter the area 
was calculated by using the methane (CH4) concentrations sampled at the discharge of the seals. Tracer 
gas was used to verify the ventilation flows through the area. 



^Mining engineer, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 
^Chief engineer, MA.E. Services Inc., Beckley, WV. 



INTRODUCTION 



A goal of the coal industry is to mjiximize the amount 
of coal removed without compromising miners' health zmd 
safety. As a mine develops, portions of the mine aie. aban- 
doned and mining moves to areas where coal production 
is feasible. To prevent explosive concentrations of gases in 
abandoned portions or gob areas, coal mine operators can 
(1) continue to ventilate them or (2) isolate them from the 
main mine ventilation system by sealing. To seal an aban- 
doned area, operators construct substantial and incombus- 
tible seals of sufficient strength to prevent their rupture in 
the event of an explosion. The conditions encountered in 
underground coal mines make it difficult to construct a 
seal that is completely airtight; recent studies indicate a 
near perfect seal will leak 150 cfm/in, w.g. Seals do, 
however, greatly restrict the passage of air in and out of 
abandoned areas. 

This report documents an investigation of an aban- 
doned sealed area in a West Virginia coal mine. The 



atmosphere behind the seals was sampled on a regular 
basis. During one of the sampling cycles, peak concen- 
trations of 2,800 ppm CO and 1,260 ppm hydrogen (Hj) 
were detected, leading MSHA to close the mine because 
of the impUed danger. The atmosphere behind the seals 
was judged sjife after COj gas was injected into the 
abandoned area. A yr later, the seals needed to be 
breached in order to continue with extraction of the seam. 
The Bureau of Mines assisted in estabhshing a gas 
sampling strategy and in collecting gas samples until the 
ail exiting the abandoned area had reached a CH4 
concentration of 1.5 pet. A tracer gas, sulfur hexafluoride 
(SFg), was used to test the ventilation in the abandoned 
area after the seals were breached. The seals were safely 
breached, and within 95 h production at the mine was 
resumed. 



BACKGROUND 



Quinland Mine, an underground coal mine in southern 
West Virginia, was opened into the Cedar Grove coal 
seam in 1973. The coalbed locally averages 42 to 50 in 
thickness and the overburden ranges from 250 to 900 ft. 
The mine used room and pillar mining with six to seven 
entries (fig. 1). The parallel mains, submains, and panels 
were developed and interconnected at the termination 
point by bleeder entries. Barrier pillars ranging from 
300 to 525 ft in width are maintained between mains, 
submains, and panels being developed. The mine is ven- 
tilated by two main fans operating parallel. One fan 
(339,000 cfm) ventilates the northern portion of the mine, 
while the other fan (212,000 cfm) ventilates the southern 
portion. CH4 liberation at this operation is approximately 
226,000 cfm in 24 h. 

The mine developed from two mains (2 East Mains). 
Two parallel north mains were developed off the 2 east 
mains. Development of 1 North Mains began in 
May 1974; development of 2 North began in May 1977. 
The 1 and 2 North Mains are interconnected by bleeder 
entries. Last reported mining in 2 North Mains was on or 
about July 1982. A ventilation survey indicated that sealing 
off 1 and 2 North would result in more effective ventilation 
in the existing workings. In August 1984, two sets of seals 



were constructed in the 1 and 2 North entries (fig. 2). The 
14 sejils were constructed of soUd concrete blocks, set on 
solid flooring and were not hitched into the ribs. The 
16-in blocks were placed with the long axis of each block 
aligned parallel to the rib along the entry length, and laid 
skin to skin with mortared joints, producing an effective 
thickness of 16 in. Seals were faced with mortar, then the 
face and perimeter were coated with a fire-resistant rigid 
foam. A valved sampling pipe was placed in the center of 
the highest number 1 seal (left) of both panels to measure 
the pressure differentiail across the seals cuid to monitor 
the atmosphere in the sealed area. The sampling pipes 
terminated approximately 5 ft inby the seals. A water 
drainpipe and trap with a shutoff valve were installed in 
the lowest elevation, at the number 7 seal of each panel. 
Supplemental roof support, such as cribs £md timbers, were 
used where needed in the 2 North aiea, because roof falls 
in the 2 North panel had occurred prior to seaUng. The 
mine firebossed the seals during preshift and during the 
weekly ventilation inspection. During an inspection in 
April 1985, two of the seals in 1 North were outgassing 
around the perimeter and through the face of the seals. 
New seeds were constructed outby the original number 3 
and 6 sesds in the same mjmner as the originjd seals. 




a. 
a 
E 

« 

e 

S 

■o 
c 
a 

c 

3 

O 

I 



3 

o> 




Scale, ft 



Figure 2.— Quinland Mine 1 and 2 North Main Seals. 



DETECTION OF MINE FIRE 



In addition to the regular inspections, MSHA inspectors 
examined the seals, assessed ventilation, and collected air 
samples from behind the 1 and 2 North seals. During one 
sampling cycle, MSHA reported the presence of CO and 
H2 in 2 North. Table 1 shows the average concentrations 
of COj, oxygen (Oj), CH4, CO, and Hj reported in 1 and 
2 North (i)/ 

The MSHA subdistrict manager requested that 
additional samples be collected at the 2 North location. 
Inspectors went imdergroimd to obtain bottle samples, 
visually inspect the seals, conduct smoke leakage tests, 
obtain hand-held sample readings at the seal face and 
outby the mmiber 1 seal, take stain measurements, obtain 
pressure differentials across the seals, and take airflow 
readings. During the inspection of the 2 North seals, air 
was foxmd to be leaking around the perimeter of the 
number 1 seal and at the water trap in number 7 seal. 
MSHA required mine management to remove miners from 
imderground, and then issued an imminent danger order 
because of the elevated levels of CO (evidence of a fire) 
and the presence of Hj in 2 North. The Jones-Trickett 
ratio (JTR) (2) was apphed to the data to provide insight 
into what was on fire. The 2 North gas samples gave a 
JTR value of 0.53,which indicates CH^ was the primary 
fuel for the fire. 

Four boreholes (table 2) were drilled from the surface 
to the 2 North panel for atmospheric sampling (fig. 3). 
Each borehole was equipped with a three-tube bundle of 
sample tubing that extended through the borehole to near 
the top, middle, and bottom of the coalbed. This arrange- 
ment was initially used because air within a sealed area 
tends to stratify. After several hr of sampling, it was 
obvious that it was uimecessary to obtain gas readings at 
the three height locations; gas concentrations were the 
same at each height. 

The number 4 borehole was sampled and gas concen- 
trations, in pet, averaged: CO2-O.8, Oj-lS.?, CH4-3.4, 
and CO-0.1. Underground, work crews collected bottle 
samples from the 2 North number 1 seal; gas concentra- 
tions, in pet, averaged: CO2-O.9, O2-I7.8, CH4-6.I, 
nitrogen (N2)-76.41, CO-0.257, and H2-O.O76. These 
individual samples prompted mine management to submit 
a formed mine fire and seunpling plan as an aid in dealing 
with the fire (appendix A). Decisions on the state of a fire 
are based on the changing composition of the mine air and 
not single samples (3). 

Because the samples collected indicated the presence 
of am explosive mixture of gases behind the 2 North seals, 
MSHA prohibited regular visits to the underground 
sampling ports. To gain information on the environment 
behind the seals, a crew of workers was given permission 
to go underground zmd install a sampUng tube from the 
number 1 seal of 2 North, 



Mine management proposed to MSHA that CO2 
gas be injected down a borehole. Thirty st (525,000 ft^) of 
CO2 gas, pumped down borehole 3, resulted in a 
nonexplosive atmosphere behind the 2 North seals. 
Miners were then permitted to go imderground to assess 
the ventilation and to apply a cementitous (gunite) sealant 
to the surfaces. When the crew arrived at 2 North, mem- 
bers observed COj leaking out of the seals. To reduce the 
leakage, they coated the seal face and ribs with gunite. 

Forty-two st (735,000 ft^) of CO2 was then pumped 
through the number 3 borehole into the area behind the 
2 North sejils. Gas analyses indicated a steady improve- 
ment of the atmosphere behind the seals. The crew of 
miners returned imderground to continue rehabiUtating the 
seals. As a safety precaution, an additional 28 st of COj 
was pumped down the number 3 borehole. A total of 
98 st CO2 (approximately 1,710,000 ft') was pumped into 
the area behind the 2 North seals to make the atmosphere 
nonexplosive. 

Five days after the initial injection of COj in the 
number 3 borehole, bottle samples collected at the number 
2 borehole had gas concentrations below the explosive 
range (table 3). The continuous gas monitoring station 

TABLE 1. - Average gas concentrations behind seals, 
percent 







1 North 


2 North 


C02 

CH." '.'.'.'.'.'.'.'.'.'.'.'.'.'.'. 

CO 

H, 




1.30 
12.35 
19.07 




Trace 


0.91 
18.62 

2.13 
.268 
.12 


Higher hydrocarbons . . 




Trace 


TABLE 2 


- Borehole descriptions 




Diameter, 
Borehole in 


Depth, 
ft 


Entry location 

in 2 North 

seals 


Distance from 

2 North seal, 

ft 


1 6 

2 6 

3 6 

4 2 


261 
269 
176 
685 


6 
3 
1 
4 


2,900 

3.050 

3,075 

310 



TABLE 3. - Gas concentrations in number 2 borehole of 
2 North after Injection of 98 st of CO2, percent 

Location Borehole 2 

CO2 9.38 

O2 11.08 

N2' 62.32 

CH4 18.19 

CO .0298 

H2 NA 

NA Not analyzed. 

'The percentage of N2 was determined by subtracting the sum of 
the reported values from 100.00. This valve is nitrogen plus argon. 



Italic numbers in parentheses refer to items in the list of references 
preceding the appendixes at the end of this report. 



660- 




LEGEND 
Borehole 
^Seal 

— Bottom of COG 
elevation lines 



Figure 3— Borehole locations In 2 North. 



samples collected immediately behind the 2 North seals 
were considered stable. The data indicated the original 
fire behind the seals was not burning, and CH4 concen- 
tration in the atmosphere at the boreholes was due to the 
holes being at a higher elevation than the seals, therefore 
the CH4 was displaced by COj. 



The closure order was terminated because a nonexplo- 
sive atmosphere now existed behind the seals. After mine 
management submitted a completion plan to MSHA 
(appendix B), the mine was reopened. 



SEAL BREACHING 



Approximately 1 yr after the start of the fire, mine 
mamagement submitted a plan to MSHA to open the seals 
in 1 and 2 North Mciins for the purpose of driving a set of 
mains off the number 7 entry in 2 North (3). The mine 
had attempted to develop a set of mains off of 2 North, 
but was unable to continue advancing because of geologic 
conditions that created roof control problems (fig. 4). For 
future development of the mine, it was necessary to brecik 
into the sealed area, establish ventilation, and begin driving 
a set of entries from the number 7 entry in 2 North. The 
Bureau was requested to estabhsh a gas samipling strategy 
to be used during the seal-breaching operation, and to 
conduct a tracer gas test to evaluate the ventilation in the 
abandoned area. 

Two 3/8-in-ID tube bundles were extended from the 
seals at 1 cmd 2 North to an outside monitoring station. 
One tube bimdle was for 1 North and the other was for 
2 North. The outside monitoring station was equipped 
with a portable gas chromatograph, sampling pumps used 
to draw samiples from behind the seals to the surface, cadi- 
bration gcis, evacuated seunple tubes, detector stain tubes, 
and hand-held gas detecting instruments. This continuous 
monitoring station made it unnecessary for individuals to 



go underground to obtain air samples. If the continuous 
monitoring station fedled, an alternative plam would have 
been followed (appendix C). 

A known concentration of calibration gas was inserted 
at the tube end to test for leakage and accuracy. Before 
taking a sample, it wjis necessary to draw the atmosphere 
through the tubing for a period not less than three times 
that required for one air exchange {4). Once started, sam- 
pling pumps operated continuously, ensuring an uninter- 
rupted air exchange. 

Some site preparation was done prior to the seal 
breaching. Mine phone communications were estabhshed 
between both seal locations and the surface. An air com- 
pressor was located in 2 North with the air Unes extending 
to the 1 and 2 North seal areas. Gunite on the number 
1 seals of both 1 and 2 North was removed from a 48- by 
48-in area using jackhammers with stimdard hardened steel 
bits. Wing curtains were installed within 10 ft of each of 
the seals to provide ventilation to sweep away any noxious 
or toxic gases emitted from behind the seals when they 
were opened. Temporary ventilation controls were 
installed in 2 East to facihtate a 0.5-in, w.g. drop between 
1 and 2 North, so that air would enter 2 North and exit 




Water drain- 
pipe and trap- 



Sccle, ft 



'~^C?o/ = Seal 



Figure 4.— Projected mine development 

1 North (fig. 5). An air volume of 35,000 cfm was mea- 
sured at the junction of 1 North and 2 East. It was calcu- 
lated that a 10-ft^ opening would be needed to ensure a 
flow of 20,000 cfm through the sealed area. 

For a period of 24 h prior to the seed breaching, gas 
concentrations behind 1 and 2 North seals were collected 
via the sampling tube for background information. As a 
caUbration check, bottle samples were also collected. The 
pressure differential across the seals prior to breakthrough 
cuid the average gas concentrations behind the seals 
collected for this 24 h period are shown in table 4. 

On the first day of miners annual vacation, Saturday, 
July 26, 1986, at 11:00 a.m. the number 1 seals in both 
1 and 2 North Mains were breached. Only personnel 
required for the seal breaking were permitted under- 
ground. Seals were breached by a certified mine fore- 
man/fireboss who performed all tests prescribed by law. 
Two persons trained in mine rescue procedures were pres- 
ent at the seals with mine rescue apparatus. All electrical 
power inby the intersection of 2 North and 2 East was shut 
off. Phone communication to the siuface was estabUshed. 
Ventilation measurements were taken at the 1 North-2 
East intersection to ensure that an air quantity of 35,000 
cfm of air was available. Hand-held gas readings, evac- 
uated tube samples, emd bottle samples were collected as 
a cahbration check for the outside monitoring station. The 
work sequence was to breach the number 1 seal of 
1 North, then advance to 2 North and breach the number 
1 seal of 2 North. If during the seal breaching, either 
mine fan failed, all persons underground would return to 
the surface and all electrical power would be deenergized. 



'O/ 



Sampling u 
pipe- 



K 
^^^, 



^0/ 
^0/ 



o 



'^mm 



Water drain- 
pipe and trap 



'a 






/so 



--^ — I- 



M^^Po^Op^^/?^ 



%M. 



-Sampling 
pipe 



^^ LEGEND 

(i^ — c~ Check curtain 
c\y ^= Seal 

X Overcast 
=^ Stopping 
— ► Return 
->♦ Intake 



^ 



400 



^ 



^ 



^ 



Scale, ft 



^, 



Figure 5.— Temporary ventilation controls in 2 East. 



Table 4. - Average gas concentrations behind seals, percent, and 
pressure differential across seals prior to breakthrough 

1 North 2 North 

CO2 3.22 1.37 

O2 6.15 13.5 

N/ 56.29 63.45 

CH4 31.11 19.89 

Other gases 3.23 1.79 

CO 

CjHg .0008 .0006 

Pressure differential . . . . in, w.g. . . +0.8 -0.37 

'Nitrogen plus argon. 

To eliminate sparking, brass tools were used to break 
the seals. The number 1 seal of 1 North was breached 
with a 4- by 2.5-ft opening. After the crew zarived at the 
2 North seals and communication was established to the 
outside, the number 1 seal of 2 North was also breached 
with a 4- by 2.5-ft opening. The air reading was taken to 
ensure that a minimum of 20,000 cfm was entering the 2 
North seal opening. One individual, using breathing 
apparatus, then went back to the 1 North opening to 
obtain measurements of pressure drop across the opening 
(0.1 in, w.g.), air volume (22,500 cfm), and concentrations 
of O2, (3.7 pet), CO, (0 ppm), and CH4 (>5 pet). After 



30 min, SF^ was released at the opening of the 2 North 
seal. All persons then exited the mine. Power was 
restored inby 2 East-2 North intersection. 

Gas concentrations were continuously recorded. The 
air volume contained in the abandoned area was calculated 
by mine engineers in an attempt to determine how long it 
would take for the return air out of the 1 North seal to 
reach a CH4 concentration of 1.5 pet. CH4 was the gas 
that was used to assess the ventilation inby the seals. No 
one was certain of the entry and roof conditions that 
existed inby the seals. Mine maps showed conditions prior 
to sealing, but how the abandoned area had been affected 
by the fire was unknown. The open volume behind the 

1 and 2 North seals was estimated as 26,676,000 ft^ (appen- 
dix D) with a ventilating airflow of 22,500 cfm entering the 

2 North seal and exiting 1 North. It was assumed that the 
air in 1 and 2 North had a known CH4 concentration of 31 
pet and that generation of CH4 had ceased. 

Depending on the equation applied, purge times were 
calculated as 20 h, 60 h (4), 120 h (5), and 138 h (<J) 
(appendix E). The CH4 concentration declines as clean air 
is substituted for contaminated air. A dilution time of 20 h 
would result from plug flow in which the volxmie of con- 
taminated air contJiined behind the seals is completely 
flushed out as an air exchange is made. This is an ideal 
situation and assimies that all the contaminated gas is 
displaced without mixing with the air. The dilution time of 
60 h is based on dilution equations presented by Hart- 
man (4), and is used to determine the time that elapses 
before a certain concentration is reached. The purge time 
of 120 h uses dilution equations commonly used in indus- 
trial ventilation (5). This situation often arises when 



confined spaces need to be ventilated to permit safe re- 
entry after contamination, and implies that the volume of 
ail required to reduce the concentration of the con- 
taminant is proportional to the contaminated volume 
space. A dilution time of 138 h assumes that a space has 
an initial concentration and air is continuously fed into the 
space; then the diluted concentration at any time will 
follow a logarithmic decay curve (7). 

Forty-nine hr after the seals were breached, the CH4 
concentration of air exiting 1 North had only dropped to 
4.8 pet, zmd mine management decided to speed up the 
dilution time. The openings in the number 1 seals of 1 
and 2 North were enlarged to 20 ft^ allowing 31,000 cfm 
of air to enter the 2 North mains and return through the 
1 North opening. Routine air sampling of the atmosphere 
in the niunber 1 and 2 North Mains continued. After the 
air volume was increased for 2 h, the CH4 concentration 
climbed to 6 pet; within 3 h after this surge, the CH4 con- 
centration dropped to 4 pet. The CH4 concentration 
reached 1.5 pet at the 1 North seal, 95 h after breaching. 
Appropriate inspections were made and the mine went 
back into production on Wednesday, July 30, 1986 at 
12:30 p.m. 

Redoing the calculations originally used for estimating 
the time for CH4 to reach 1.5 pet and accounting for the 
increase in jiirflow after 49 h, the previous calculated 
dilution times are recalculated as 14 h, 54 h (4), 107 h (5), 
and 117 h (<5) (appendix F). The industrial ventilation 
equation used to calculate the purge time required to 
saifely enter a confined space (107 h) gave the closest 
approximation of the actual dilution time (95 h). 



USING TRACER GAS TO UNDERSTAND AIR MIGRATION PATTERNS 

THROUGH ABANDONED AREA 



SFg was used as an aid to understanding the migration 
patterns through the sealed area. SF^ is colorless, odor- 
less, chemically and thermally stable, and can easily be 
introduced into an airstream (7-8). SF^ is contained in 
metal pressurized cylinders, which are pressured to 300 psi, 
equivalent to approamately 1.5 ft^ of gas at atmospheric 
pressure. Since SFg does not occur naturally in the 
environment, background concentrations are no problem. 
SFg samples are collected in evacuated 10- or 20-mL test 
tubes. Samples are returned to the laboratory, where 
0.1 mL of the sample is drawn with a syringe and injected 
into an electron capture gas chromatograph for analysis. 

Thirty minutes after the 2 North seals were breached, 
a known voliune of SF^, 30.0 L, was released into the air- 
stream at 2 North. The mass of SFg recovered in the 
return eiir exiting 1 North was determined to be 28.1 L, 
which is nearly equivalent to the amount released. An 
example of this recovery calculation is presented in 
appendix G. 

Figure 6 shows a concentration curve for SF^ exhausting 
from the 1 North opening as a function of time. SF^ was 
released in an airstream having an air velocity of 



2,258 fpm, which created adequate mixing of SFg at that 
location. SF^ was first detected exiting at 1 North 10.8 h 
after it was released in 2 North, and SF^ continued to exist 
at the samphng location in the 1 North seals for a period 
of 90.8 h after release, at which time sampling ended. The 
straight-line path for air from 2 North to 1 North is 
12,000 ft. This travel length divided by SFg arrival time 
gives an air velocity of 18.7 fpm. 

Assuming different stopping conditions behind the seals, 
different average velocities could have been calculated. In 
one assumed case, there are two connected entries inby 
the breached seal that are separated from the other five 
entries by a stopping line. Equivalent entries are used to 
accoimt for the crosscut space between these two parallel 
entries. Assuming that all stoppings through this area 
offer quality construction and minimum leakage, the veloc- 
ity through these two entries would be 82.3 fpm (appen- 
dix H). In the second assumed case, all seven entries are 
functioning as aircourses with normal mine leakage at each 
of the stoppings. Since it is assumed that each entry is an 
aircourse, there is no migration of air into crosscuts and 
crosscut space is not taken into consideration. The 



100 



E 

Q. 
Q. 



o 

a: 

\- 
-z. 

UJ 

z 
o 

Li_ 
CO 



10 



KEY 
X Sulfur hexafluoride, SFg 



Airflow Increased 

22,500 31,000 

cfm cfm 




-X-*- 



J_ 



_L 



J 1 I L 



J I L 



5 10 15 20 25 30 35 40 45 50 55 

Saturday, July 26, 1986 Sundoy, July 27, 1986 Monday, July 28, 1986 

RUN TIME, h 

Figure 6.— SF^ concentration in 1 North. 



60 65 70 75 80 85 

Tuesday, July 29, 1986 



velocity through these entries becomes 32.1 fpm. In the 
third assumed case, the stopping hnes are not intact 
because of the fire or because of roof falls. In this 
situation, once again, equivalent entries should be used to 
determine the average velocity through the total volimie, 
which becomes 19.7 fpm. After an investigation inby the 
seals, some stoppings between entries were foimd to have 
been destroyed because of the shock wave created by 
forces of the explosion or fire (2). In this situation, the 
use of equivalent entries to calculate the velocity of the 
area behind the seals (19.7 fpm) closely approximates the 
travel velocity of SFg (18.7 fpm). 

Figure 7 shows CH^ levels plotted as a function of time. 
The concentration of CH4 exiting the 1 North sezd re- 
mained relatively constjmt for a period of 12.3 h, before 
beginning to decrease. The arrival time of SF^ at the 
1 North opening was 10.8 h, which is relatively close to 
the 12.3-h initial decrease time of CH4. After 12.3 h CH^ 
concentration was found to decay exponentially, but with 
a chjmge in slope aifter 43.5 h; this change in slope is 
attributed to eddy zones (9) that could cause problems in 
data interpretation. The ventilating area behind the seals 



had zones of CH^ laden air, well zmd poorly mixed with 
fresh air. After 43.5 h, CH4 concentration reached a 
constant slope. Use of the initial slope as a means to 
predict a time when CH4 would have reached 1.5 pet 
woiJd have resulted in an incorrect prediction. 

Tracer gas can be used as a tool to understand the 
conditions inby a set of seals, should future openings in 
other abandoned areas be necessary. The tracer gas, in 
conjunction with CH4, provides insight to the conditions 
inby the seals. The CO2 decay ciure could have been used 
in the same manner as the CH4 concentration information. 
Concentrations of the other gases were not high enough to 
be used to interpret trends. 

The SFg decay curve (fig. 6) and the CH4 decay curve 
(fig. 7) do not have the same slope. The concentration of 
CH4 that existed inby the seals was distributed through all 
entries and crosscuts. As fresh air passed through the 
section, CH4 was continuously diffusing from other entries 
into the main flow stream. The SFg was injected into the 
moving eiirstream zmd did not get coursed to all the back 
entries behind the seals. The SFg decay curve indicates 
that different flow paths exist behind the seals. 



10 



n 1 1 1 1 1 1 r 



n 1 1 1 1 r 



-I r 



SFg arrives 



KEY 

Methane 



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o 






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5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 

Saturday, July 26, 1986 Sunday, July 27, 1986 Mondoy, July 28, 1986 Tuesday, July 29, 1986 Wednesday, July 30, 1986 

RUN TIME, h 



Figure 7— 1 North CH4 decay curve. 



PREDICTING GAS CONCENTRATIONS 



From the time the seals were breached until CH4 levels 
reached 1.5 pet the following gases were continuously 
sampled: CO, COj, O2, and CH4. Nj level was determined 
by subtracting the sum of the reported values from 100.00. 
Because the critical gas was CH4, the portable gas 
chromatograph only sampled for CH4. Evacuated bottle 
samples were collected for anzdysis of other gases by a 
laboratory gas chromatograph. Bottle samples were 
collected continuously for 24 h before and during 
breaching of the seals and until the CH4 exiting the 
1 North seal reached 1.5 pet. The concentrations of COj, 
CO, O2, and Nj as a function of time are shown in 
figure 8. 

When using gas concentrations as indicators of existing 
conditions, it is importemt to look at long-term trends, as 
opposed to single numbers. The Bureau's continuous 
monitoring system made on-site data interpretation 
possible. To predict trends, semilogarithmic graph paper 
was used to plot instantaneous CH4 gas concentrations 
versus time data (fig. 6). Three days after the seals were 
opened, the CH4 concentration exiting the 1 North opening 
was less than 5 pet and CO concentration was ppm. 
Because these concentrations indicated an explosion was 



not possible, mine management requested that a ven- 
tilation change be made. The 1 and 2 North seal openings 
were enlzu-ged to 20 ft^ allowing 31,000 cfm of air to enter 
the 2 North mains emd return through the 1 North 
opening. Two hours after the air volume was increased, 
the CH4 concentration rose to 6 pet. Within 3 h after this 
CH4 surge, the concentration approached 4 pet. After 
realizing that there were different slopes for CH4 decay, 
the Bureau was able to collect data and extrapolate a time 
when CH4 would reach 1.5 pet. The change in slope 
occurred before an increase in air volume was made. 
Using the data plotted on semilogarithmic paper when 
CH4 would reach 1.5 pet, it was estimated that it would 
occur 99 h aifter the seals were breached and ventilation 
was estabUshed. 

In reahty, the concentration of CH4 reached 1.5 pet in 
95 h, a 4.2-pct difference from the predicted value, which 
indicates that sampled gas data can be effectively used to 
extrapolate future gas concentrations. After a trend has 
been established and is well defined, one can mathemati- 
cally derive the time for a gas concentration to reach a 
certain level using appropriate equations. 



11 



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80 


85 90 95 100 


Saturday, July 26, 1986 


Sunday, July 27, 1986 Monday, July 28, 1986 Tuesday, July 29, 1986 

RUN TIME, h 

Figure 8.-Concentration in 1 Nortli-COj, Oj, N2, and CO. 




Wednesday, July 30, 1986 



DISCUSSION 



Gases considered typical of those from a fire were 
detected behind a sealed area in a producing coal mine, 
which caused MSHA to require the mine operator to take 
actions to remedy the situation immediately. When the 
analjtical results of air Scimples collected from the sealed 
area were incorporated into the JTR, the results showed 
that CH4 was the probable fuel. Boreholes were drilled 
into the seaded area to collect air samples to interpret what 
was occurring. Because the activity occurring in the sealed 
area was stable, and nothing supported a beUef that the 
fire might be spreading, mine management's goal was to 
create a nonexplosive atmosphere behind the seals and 
return the mine to production status. Because CO2 gas 
seeks an area of low elevation, it was pumped down a 
borehole and traveled to the low elevation sampling cu^ea 
estabUshed behind the seals. This created a nonexplosive 
atmosphere in the sealed area, and the mine was returned 



to production. Approximately 1 yr later, mine manage- 
ment submitted a plan to MSHA to breach the seals. The 
Bureau was requested to estabUsh a samphng strategy, 
study airflow migration in the zu-ea using a tracer gas, and 
monitor the atmosphere in the abandoned area until the 
return air contained less than 1.5 pet CH4. 

No one was certain of the airflow patterns that existed 
inby the seals. Mine maps showed ventilation controls and 
known falls, but how the abandoned area was affected by 
the fire was unknown. Purge times were estimated using 
different equations. On the assumption that CH4 genera- 
tion had ceased behind the seals and using an estimated 
volume, the industrial ventilation equation provided the 
closest approximation to the actual time in which CH^ 
reached 1.5 pet. SF^ tracer gas was used to determine the 
air migration patterns through the abandoned area. In this 
situation, SFg was used to determine the velocity of air 



12 



through the sealed area and to understand the CH4 rate of 
decay from the 1 North exit. CH4 exiting the sealed area 
followed a logarithmic decay ctirve but with a change in 
slope. This phenomenon is due to eddy zones that exist in 
mines. COj could have been used in the same manner; 
the other gases (Oj, CO, and Nj) were not sufficient to use 
in estabUshing a trend for use in understanding the eddy 
zones within the sealed area. 

For proper decisionmaking throughout a mine fire (or 
other events that are atypical of a mine's daily routine, 
such as seal breaching), it is essential to have reliable gas 
sampling information. Computations, diagrams and 
common sense are used as aides in imderstemding and 
interpreting the situation. Repeated gas sampling of an 
environment permits forecasting trends and evaluating the 



effectiveness of a change. During the seal breaching 
operation, a change was made approjdmately 2 days after 
the seals were opened. When CH4 concentration exiting 
the return opening was below the lower explosive limit 
(5 pet) mine management, wanting to expedite the dilution 
process, arranged to go imderground to enlarge the seal 
openings to permit 40 pet more air through this section. 
The CH4 concentration 1 North return air reached 1.5 pet 
46 h after the airflow through the area was increased. 
Because gas samples were continuously collected, analyzed, 
and plotted, it was possible to evaluate how effective a 
change was on the return atmosphere. Data interpreters 
should be aware that abrupt chzmges can occur, therefore, 
continuous, long-term data must be used to understand 
and evaluate changes. 



SUMMARY 



After an investigation, it was determined that an 
explosion had occiu-red behind the sealed area of the 
Quinland Mine (10). The fire situation caused the mine to 
be placed under a closure order. After 98 st of CO2 was 
pumped into the sealed area, the atmosphere behind the 
seals was considered stable and the mine returned to full 
production. 

Approximately 1 yr later, mine management submitted 
a request to breach the seals. The Bureau was requested 
to estabUsh a samipling strategy and monitor the 
atmosphere in the abandoned area imtil the return air con- 
tained less than 1.5 pet CH4, Continuously monitoring the 
CH4 gas amd plotting the results, showed that after 49 h 
CH4 concentration exiting the abandoned area was below 
the explosive range. The seal openings were increased to 
allow an airflow of 31,000 cfm to enter the area. Within 
46 h after the airflow change, CH4 concentration exiting 



the opening reached 1.5 pet. The continuous sampling of 
return gases and their proper interpretation allowed safe 
decisions to be made on the ventilation air in the 
abandoned area. Tracer gas was used to aid in 
understanding flow paths through the area.. In future 
operations, SFg can help to solve ventilation analysis 
problems that do not respond to conventional methods 
analysis; its application should be considered when such 
problems are encountered. Other mine operators have 
used modified techniques before breaching seals. This 
procedure requires that the area adjacent to the seals be 
inerted with N2 (this involves an airlock with a set of 
temporary stoppings built out by the seals). The recovery 
team using brass tools and under breathing apparatus 
would breach the seals. With this method, an inert 
atmosphere was assumed on both sides of the seals (high 
CH4 on one side and high Nj on the other). 



REFERENCES 



1. Davis, J. E. Report of Investigation (Underground Coal Mine 
Fire), Quinland No. 1 Mine, MSHA, District 4, July 18, 1985, 22 pp.; 
available from J. M. Krese, MSHA, Mount Hope, WV. 

2. David, J. W. Addendum to Report of Investigation 
(Underground Coal Mine Fire), Quinland No. 1 Mine, MSHA, 
District 4, Oct. 31, 1986, 4 pp.; available from J. M. Krese, MSHA, 
Mount Hope, WV. 

3. Mitchell, D. W., and F. A. Bums. Interpreting the State of a 
Mine Fire. MSHA IR 1103, 1979, 18 pp. 

4. Hartman, H. L. Mine Ventilation and Air Conditioning. Wiley, 
1961, 398 pp. 

5. Guffey, S. E. Unpublished class notes on Industrial Ventilation, 
Univ. Toledo, Toledo, OH, 1983; available upon request from 
D. M. Doyle-Coombs, BuMines, Pittsburgh, PA. 



6. Mateer, R. S. Unpublished class notes on Industrial Ventilation, 
University of Kentucky, Lexington, KY, 1979; available upon request 
from D. M. Doyle-Coombs, BuMines, Pittsburgh, PA. 

7. Turk, A., S. M. Edmonds, H. L. Mark, and G. G. Collins. Sulfur 
Hexafluoride as a Gas-Air Tracer. Environ. Sci. Tech., v. 2, No. 1, 
1968, pp. 44-48. 

8. Froger, M. C. Detection and Measurement of Stray Air 
Currents. Centre d'etudes et Recherches des Charbonnages de France, 
Annex III, 1967, 18 pp. 

9. Kissell, F. N., and R. J. Bielicki. Ventilation Eddy Zones at a 
Model Coal Mine Working Face. BuMines RI 7991, 1974, 14 pp. 

10. Miller, E. J. Recent Explosions in Inaccessible Areas of 
Underground Coal Mines. Paper in Proceedings of the Third U.S. 
Mine Ventilation Symposium (State College, PA). 1987, p. 240. 



APPENDIX A.-MINE FIRE SAMPLING PLAN 

Samples of the atmosphere behind seals in 1 and 2 North off 2 East Mams are to be taken in accordance with the 
procedures given below. The person taking samples should report any sampUng that deviates from one or more of these 
procedures; i.e., the person should record the seimple niunber and manner by which it deviates, and that record should 
be made part of the analysis and should be noted in the remarks coliunn of the computer printout of gas-sample data. 

Procedxu'es 

A. Three lines of 1/4-in-ID, semirigid sampling tubing in a closed bundle extend from the surface through each 
borehole into 2 North. One tube (floor) will be 1 ft above the bottom (a point that might be above as well as on the 
floor); a second tube (midheight) will be 2 ft above the bottom; a third tube (roof) will be 3 ft above the bottom. 

1. Each tube shall be labeled by borehole and location. For example, 1-F is the floor tube on borehole 1. 

B. Samples shall be taken ONLy when a magnahelic of other pressure differential gauge indicates NO NEGATIVE 
pressure on the tube for which a sample is intended to be drawn. 

1. The pressure reading shall be recorded. 

C. At least two samples complying with B above shall be taken at least once every 4 h from each sampling tube 
(3 tubes by 4 boreholes by 2 = 24 samples). 

1. Each sample shall be labeled by date, time, location, and sample niunber. 

D. A sample shall be taken ONLY after the atmosphere is drawn through the sjimpling tube for a period of not less 
than 1 min using the 12-V dc pump. 

E. Each sample shall be analyzed using a gas chromatograph that has been calibrated that day using a standard 
traceable to National Bureau of Standards. 

1. The chromatograph operator shall reanalyze CO in samples containing more than 10 pet CH4 plus higher 
hydrocarbons. 

F. The results of each sample shedl be reported to mine management's authorized representative. 

1. The data shall be entered into the computer. 

2. The data shall be reported by 

Borehole. 

Location. 

Date. 

Time. 

Hydrogen (H2), percent. 

Carbon monoxide (CO), percent. 

Oxygen (Oj), percent. 

Methane (CH4), percent. 

Other hydrocarbons (C^HJ, percent. 

Nitrogen (Nj) plus argon, percent. 

Carbon dioxide (COj), percent. 

Jones-Trickett ratio (JTR): JTR = [(COj + 0.75 CO) - (0.25 H2 + 0.25 C^^)]/(0.265 N2 - O2). 

Fuel (F): When JTR is less than 0.4 F = None; JTR = 0.4-0.54, F= CH^; JTR = 0.55-0.8, F = coal or CH4; 
JTR = 0.8-1.0, F = Coal; JTR = 1,0-1.6, F = wood; JTR is greater than 1.6, F = bad sample. 

Effective combustible (EC): EC = CH4 + C^^ + 1.25 H2 + 0.4 CO. 

f CH + C JI ^ 

ExplosibiUty (Ex): Ex = EC(02/MA0) where maximum allowable oxygen, MAO = 5 + 7 '* r^P 



CH4 + c^^ + CO ■ 



14 



0-, (CO X 100) 
Relative intensity (RI): RI + 1 - 3.8 r-f ^^ - 



N2 (0.265 N2 - O2) 

CO2 - Blackdamp = (^/3.111 + 0.01 R + 0.01 S), 

where R = CO2/(0.265 N^-Oj) 

and S = CO/(0.265 N2-O2). 

Remarks 

G. The fire is out when all samples taken in six consecutive sampling periods show F = none or O2 less than 12 pet 
and RI is decreasing. 

NOTE: A fire in which CH4 is the principal fiiel produces little or no carbon residue such as soots, cokes, or char- 
coals. CO, after a fire is extinguished, disappears by 

1. Reventilation, and 

2. Absorption by carbon residue primarily, coal secondarily. 

Therefore, unless 2 North is reventilated or the fire consumed considerable coal, one should expect CO to decrease 
at a slow rate. CO, therefore, should not be used as a critical factor in decisionmaking, unless the CO concentration is 
rising. 



15 

APPENDIX B.-COMPLETION PLAN 

1. Remove any temporary ventilation controls. 

2. Conduct preshift examination of the entire mine. 

3. Complete the work of applying gunite to the number 1 and 2 North seals, and to the roof and cocd ribs of the 
blocks of coal containing the seals. 

4. Grout number 1 and 4 boreholes. 

5. Maintain nimiber 2 and 3 boreholes for sampling and for pimiprng additional COj if needed. 

6. Return the mine to production status within 5 days. 

7. Collect bottle samples daily at 2 North seal and number 2 borehole until CH4 concentration is greater than 16.0 pet 
and O2 is less than 10 pet, and then sample once a week. Continue collecting air samples at number 4 borehole until 
notified by MSHA to discontinue. 



16 



APPENDIX C.-MSHA APPROVED PLAN FOR MINE UNSEALING 
IF CONTINUOUS MONITORING SYSTEM FAILED 



After 24 h, three certified personnel shzill reenter the 
mine and check permanent checkpoints, A and B. (fig. C- 
1). Should the air contain less than 1 pet CH4 and less 
them 0.5 pet COj in the immediate return, the complete 
mine shall be firebossed and normal work carried out. 
These established checkpoints (A and B) will be checked 
weekly and recorded. 

Because of the existing ventilation controls in this 
section, the entire area inby 1 North and 2 North is being 
ventilated, because stoppings and falls direct air in the 
entries and gas concentrations can be safely evaluated at 
these established points. After the area has been flushed, 
the remaining seals in 2 North Mains shall be removed. 
The 2 North Mains shall then be rehabilitated and 
permanent checkpoint B moved inby Big Daddy Mains. 

Should bottle samples taken from checkpoint A or B 
indicate a rekindling of the fire, the area should be 
resealed COj injected in borehole 2 or 3. A certain 
amount of CO is still known to exist in the sealed regions 
because it shows up periodically in MSHA bottle samples. 
A certain amount is expected to be flushed out. Should a 
steady increase in CO (and possibly H2) indicate a 
rekindling, the area should be immediately seeded. Should 
the area not be flushed, an on-site meeting will be 
conducted to determine what secondary procedures can be 
implemented to expedite the flushing of the seal 
re^ons-such as enlarging the opening in the 2 North seal 
and/or adding additional restrictions across the 1 East 
Mains returns to force more eiir into the seals. Bottle 
samples shall be taken daily for 2 weeks and sent to 
MSHA's Mt. Hope, WV, Laboratory. The evaluation 
checkpoints A and B shall be used solely in evaluating the 
entire sealed region. A determination shall be made at a 
later date as to whether these two points are sufficient 
(long term), or one of two of the following options will 
have to be instituted. 

1. Rehabilitate 1 North to estabhsh a bleeder 
checkpoint and rehabilitate 2 North Mains inby Big Daddy 
Mains to estabhsh the water level in 3 East and 4 East as 
well as bleeder check points. 



2. 1 North shcdl be resealed at its present location, 
and 2 North shall be resealed inby Big Daddy Mains. 

After the seals have been broken and the area is 
bleeding normally, the power shall be reenergized and the 
1 North and 2 North areas be flushed 24 h prior to 
checking the newly estabUshed permanent checkpoints at 
1 North and 2 North Mains. 



e#?^'' 







LEGEND 
Checkpoint 







400 

_J 



Scale, ft 



Figure C-1 .—Location of checlcpoints. 



17 



APPENDIX D.-VOLUME CALCULATION BEHIND SEALED AREA 

Total length of airway: 23,400 ft 

Average seam height: 5 ft 

Average seam width: 20 ft 

Equivalent entries: Nmnber of entries = 7 

Number of crosscuts = 6 

Crosscuts = 75 ft centers 

Entries = 55 ft centers 

7 + [6 (55/75)] = 11.4 

Volume = 23,400 ftx5ftx20ftx 11.4 = 26,676,000 ft^ 



18 



APPENDIX E.-CALCULATIONS OF PURGE TIMES 

Plug flow: Assume that fresh air displaces ambient gas without mixing. 

Volume 
Airflow 



Hartman (4):^ 



where 



Y = 26,676,000 ft^ 
= 22,500 cfm, 
t = time, min, 



Qg -0' 



login 7^ 



0„ - Ox t O , 



Q - Qxq 2.303 Y 



X = 31 pet, 

Xq = 1.5 pet, 

and time = 3,591 min = 60 h. 

Guffey (5): 

where R = 26,676,000 ft^, 

Cj = 31 pet, 

M = mixing factor = 2, 

C( = 1.5 pet, 

G = cfm, 

O = 22,500 cfm, 

and time = 7,181 min = 120 h. 

Mateer (d): 

Dilution follows a logarithmic decay curve: 



t = [R(M)/Q] hi (Ci/q) 



Time = 8,274 mm = 138 h. 



Italic numbers in parentheses refer to items in the list of references preceding appendix A. 



19 



APPENDIX F.-CALCULATIONS OF PURGE TIME AFTER INCREASE IN AIR VOLUME 

Plug flow: Assume that fresh air displaees ambient gas without mbdng. 

Volume 
Airflow 



Hartman (4):^ 



Guffey (5): 



logio ^ 



Q„-Qx 



t Q 



Y 


= 26,676,000 ft', 


Y 


Q 


= 22,500 cfm. 


Q 


t 


= time, min. 


t 


Qg 


= 0, 


Q 


X 


= 31 pet. 


X 


Xo 


= 4.8 pet. 


Xo 



timej = 2,212 min. 



Og-Oxo 2.303 Y 
- 26,676,000 ft^, 
= 31,000 cfm, 
= time, min, 
= 0, 

= 4.8 pet, 
= 1.5 pet, 
timCj = 1,001 min. 
Total time = time^ + time2 = 3,213 min = 54 h. 



R 



= 26,676,000 ft', 

= 31 pet, Ci 

M = mixing factor = 2, M 

C, = 4.8 pet, Q 

G =0 cfm, G 

Q = 22,500 cfm, Q 



timCi = 4,423 min. 



t = [R(M)/Q] hi (Ci/q) 
R = 26,676,000 ft', 

= 4.8 pet, 

= mixing factor = 2, 
= 1.5 pet, 
= cfm, 
= 31,000 cfm, 
= 2,002 mm, 



tune. 



Total time = timej + time2 = 6,425 min - 107 h 



Mateer (6): 



Dilution follows a logarithmic decay curve. During the fourth air exchamge the airflow was increased from 22,500 to 
31,000 cfm. 

Time = 6,999 min = 117 h. 



italic numbers in parentheses refer to items in the list of references preceding appendix A. 



20 

APPENDIX G.-TRACER GAS RELEASED AT 2 NORTH AND RECOVERED 

AT 1 NORTH 

A known volume of SFg was released in the opening of 2 North. The mass of the released gas was determined using 
the change in mass of the pressurized cylinder. 

Mass of SFg released = 195.5 g per molecular weight of SF^ = 146.1 g/mol 

195.5 g 
Moles of SFg released = 145 1 g/mol ~ ^"^ °^°^ 

Volume per mol = 22.4 L 

1.34 mol X 22.4 L/mol = 29.9 L = volume of SF^ released. 

The mass of SF^ recovered at 1 North was determined by adding all the SF^ that was recovered at 1 North and 
dividing that by the number of szunples in which a measwable quantity of SF^ was present. The average concentration 
of SFg for the sampling period of 5,445 min was equal to 0.00809 ppm. Knowing the average concentration, the airflow 
volimie exiting 1 North, and the sampling time, one is able to calculate the amount that was recovered: 

0.00809 X lOE-6 ft^ SFg/ft^ air x 22,580 cfm x 5,445 min x 28.2 L/ft^ = 28.1 L = volume of SF^ recovered. 

The SFg volume recovered is nearly equivalent to the junount released. 



21 

APPENDIX H.-VELOCITY CALCULATIONS INBY SEALS 

Case 1: Behind the number 1 opening in 2 North were two interconnected entries separated from other entries by 
a stopping line. Assume no leakage. 

Air volume: 22,500 cfm 

Equivalent entries: 2 + 1(55/75) = 2.73 

Entry width: 20 ft 

Entry height: 5 ft 

Velocity = 22,500 cfm / (2.73 x 20 ft x 5 ft) = 82.3 fpm 

Case 2: Normal leakage exists in all stopping inby the seals. 

Air volume: 22,500 cfm 

Entries: 7 

Entry width: 20 ft 

Entry height: 5 ft 

Velocity = 22,500 cfm / (7 x 20 ft x 5 ft) = 32.1 fpm 

Case 3: The stoppings inby the seals are not intact-destroyed. Equivalent entries are used to account for the space 
in the crosscuts. 

Air volume: 22,500 cfm 

Equivalent entries: 7 + 6(55/75) = 11.4 

Entry width: 20 ft 

Entry height: 5 ft 

Velocity - 22,500 cfm / (11.4 x 20 ft x 5 ft) = 19.7 fpm. 



* U.S. GOVERNMENT PRINTING OFFICE: 611-012/00,023 

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